Recent developments in x-ray computerized tomography (XCT) imaging and computational simulation have made it possible to characterize the properties of asphalt concrete through reconstructing its three-dimensional (3D) microstructure and computational simulation based on the 3D microstructure. The digital representation of the real 3D microstructure (not a simulated 3D or 2D microstructure) of a physical specimen is named Digital Specimen. It is the digital counterpart of the physical specimen in every required detail. A digital specimen is usually represented as a 3D digital image and naturally includes scientific visualization of the initial/evolved microstructures and behavior related to rutting, fatigue cracking, and thermal cracking. Figures 1a and 1b are digital representations of a gyratory specimen with emphasis on its aggregate skeleton structure and its void structure, respectively. A digital specimen can be transferred through the Internet and shared by many researchers for use in multi-purpose studies such as model verification and behavior simulation. With detailed representation of the microstructure of asphalt concrete, modeling and simulation can be based on the real microstructure of the material; and experimental observation of the microstructure evolution can be compared with computational simulation to validate the models and the understanding of the fundamental mechanisms of strength and deformation of asphalt concrete.
Computational simulation of a mechanical test, which is based on digital specimens and considers every required detail of the microstructure and its evolution, is named Digital Test. It is different from conventional computational simulations that assume either a continuum model or a simulated microstructure. Figures 1c and 1d illustrate computational simulation of the digital specimen under axial loading and diametrical loading, or the digital counterparts of triaxial compression test and indirect tensile test, respectively. One can perform different digital tests on the same digital specimen, representing its multiple functional roles. The overall objective of this research is to develop Digital Specimen and Digital Test techniques and demonstrate their applications in performance evaluation of asphalt concrete.
